An exhaust gas recirculation system may be used to reduce the generation of undesirable pollutant gases during the operation of internal combustion engines. Exhaust gas recirculation systems generally recirculate exhaust gas generated during the combustion process into the intake air supply of the internal combustion engine. The exhaust gas introduced into the engine cylinders displaces a volume of the intake air supply that would otherwise be available for oxygen. Reduced oxygen concentrations lower the maximum combustion temperatures within the cylinders and slow the chemical reactions of the combustion process, which decreases the formation of oxides of nitrogen (NOx).
Some internal combustion engines having an exhaust gas recirculation system include an exhaust restriction valve for controlling the amount of exhaust gas that is diverted to the exhaust gas recirculation system and an exhaust gas recirculation control valve for controlling the amount of exhaust gas that passes through the exhaust gas recirculation system. A control system may be used to control the operation of the exhaust restriction valve as well as the exhaust gas recirculation control valve. Proper control of the exhaust restriction valve and the exhaust gas recirculation control valve is desirable to optimize engine performance and minimize pollutants.
U.S. Pat. No. 6,698,717 discloses a butterfly valve for use with an internal combustion engine having an exhaust gas recirculation system. The bore of the butterfly valve is configured to improve gas flow control sensitivity and to reduce or eliminate the unwanted passage of exhaust gas through the valve.
The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the innovations described herein nor to limit or expand the prior art discussed. Thus the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use with the innovations described herein, nor is it intended to indicate any element, including solving the motivating problem, to be essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims.